如何在JavaFX中将标签迭代添加到GridPane？

Question

我正在尝试使用for循环在JavaFX中迭代地向GridPane添加标签，但当我尝试启动应用程序时，我一直收到错误。控制台输出是：

Exception in Application start method
Exception in thread "main" java.lang.RuntimeException: Exception in Application start method
    at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:917)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$1(LauncherImpl.java:182)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.IllegalArgumentException: Children: duplicate children added: parent = Grid hgap=10.0, vgap=10.0, alignment=TOP_CENTER
    at javafx.scene.Parent$2.onProposedChange(Parent.java:454)
    at com.sun.javafx.collections.VetoableListDecorator.add(VetoableListDecorator.java:206)
    at javafx.scene.layout.GridPane.add(GridPane.java:965)
    at com.comsci.drt.ProjectGUI.start(ProjectGUI.java:181)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$8(LauncherImpl.java:863)
    at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$7(PlatformImpl.java:326)
    at com.sun.javafx.application.PlatformImpl.lambda$null$5(PlatformImpl.java:295)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.application.PlatformImpl.lambda$runLater$6(PlatformImpl.java:294)
    at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
    at com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method)
    at com.sun.glass.ui.gtk.GtkApplication.lambda$null$5(GtkApplication.java:139)

我是这方面的初学者，但我明白它告诉我，我正在尝试放置一个已经放置的物体。

代码：

Label l = new Label();
for(int i = 2; i <= 3; i++) {
    l.setText(finalResultsArray[i].getTeamName());   <-- line 181
    pane1.add(l, 0, i);
}

然后我继续使用一个标签数组，我相信它不会试图替换一个已经放置的对象，但是我收到了另一个错误:

Exception in Application start method
Exception in thread "main" java.lang.RuntimeException: Exception in Application start method
    at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:917)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$1(LauncherImpl.java:182)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException
    at com.comsci.drt.ProjectGUI.start(ProjectGUI.java:175)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$8(LauncherImpl.java:863)
    at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$7(PlatformImpl.java:326)
    at com.sun.javafx.application.PlatformImpl.lambda$null$5(PlatformImpl.java:295)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.application.PlatformImpl.lambda$runLater$6(PlatformImpl.java:294)
    at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
    at com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method)
    at com.sun.glass.ui.gtk.GtkApplication.lambda$null$5(GtkApplication.java:139)

代码：

Label[] label = new Label[12];
for(int i = 0; i < 12; i++) {
    for(int j = 0; j < 1; j++) {
        label[i].setText(finalResultsArray[i].getTeamName());
        pane1.add(label[i], 0, i);
    }
}

Answer 1

您需要为每个标签调用一个构造函数。对于您的第一个片段，只需在循环中移动“new Label”调用。

Answer 2

每次想要向网格中添加文本时，都需要使用一个新的< code>Label实例。此外，新创建的数组用< code>null值填充。

因此，使这项工作成为可能的方法是

for(int i = 2; i <= 3; i++) {
    Label l = new Label();
    l.setText(finalResultsArray[i].getTeamName());
    pane1.add(l, 0, i);
}

或

Label[] label = new Label[12];
for(int i = 0; i < 12; i++) {
    label[i] = new Label();
    label[i].setText(finalResultsArray[i].getTeamName());
    pane1.add(label[i], 0, i);
}